Imprint lithography

ABSTRACT

An imprint lithography apparatus is disclosed that has a first array of template holders, a second array of template holders, and a substrate table arranged to support a substrate to be imprinted, wherein the first array of template holders is arranged to hold an array of imprint templates that can be used to imprint a first array of patterns onto the substrate, and the second array of template holders is arranged hold an array of imprint templates that can be used to imprint a second array of patterns onto the substrate, the patterns imprinted by the second array being interspersed between the patterns imprinted by the first array.

1. FIELD

The present invention relates to imprint lithography.

2. BACKGROUND

A lithographic apparatus is a machine that applies a desired patternonto a target portion of a substrate. Lithographic apparatus areconventionally used, for example, in the manufacture of integratedcircuits (ICs), flat panel displays and other devices involving finestructures.

It is desirable to reduce the size of features in a lithographic patternbecause this allows for a greater density of features on a givensubstrate area. In photolithography, the increased resolution may beachieved by using radiation of shorter wavelength. However, there areproblems associated with such reductions. Current systems are startingto adopt optical sources with wavelengths in the 193 nm regime but evenat this level, diffraction limitations become a barrier. At lowerwavelengths, e.g. extreme UV with a length of 13.5 nm, the transparencyof materials is very poor and reflective optics must be used. As theoptics only function in ultra high vacuum such optical lithographymachines capable of enhanced resolutions require complex optics, ultrahigh vacuum systems and rare materials and are consequently veryexpensive.

An alternative for printing sub-100 nm features, known as imprintlithography, comprises transferring a pattern to a substrate byimprinting a pattern into an imprintable medium using a physical mouldor template. The imprintable medium may be the substrate or a materialcoated on to a surface of the substrate. The imprintable medium may befunctional or may be used as a “mask” to transfer a pattern to anunderlying surface. The imprintable medium may, for instance, beprovided as a resist deposited on a substrate, such as a semiconductormaterial, into which the pattern defined by the template is to betransferred. Imprint lithography is thus essentially a moulding processon a micrometer or nanometer scale in which the topography of a templatedefines the pattern created on a substrate. Patterns may be layered aswith optical lithography processes so that, in principle, imprintlithography could be used for such applications as IC manufacture.

The resolution of imprint lithography is limited only by the resolutionof the template fabrication process. For instance, imprint lithographymay be used to produce features in the sub-50 nm range withsignificantly improved resolution and line edge roughness compared tothat achievable with conventional optical lithography processes. Inaddition, imprint processes do not require expensive optics, advancedillumination sources or specialized resist materials typically requiredby optical lithography processes.

Current imprint lithography processes can have one or more drawbacks aswill be mentioned below, particularly with regard to achieving overlayaccuracy and/or high throughput. However, significant improvement inresolution and line edge roughness attainable from imprint lithographyis a strong driver for addressing those and other problems.

3. SUMMARY

According to a first aspect of the present invention, there is providedan imprint lithography apparatus comprising a first array of templateholders, a second array of template holders, and a substrate tablearranged to support a substrate to be imprinted, wherein the first arrayof template holders is arranged to hold an array of imprint templatesthat can be used to imprint a first array of patterns onto thesubstrate, and the second array of template holders is arranged hold anarray of imprint templates that can be used to imprint a second array ofpatterns onto the substrate, the patterns imprinted by the second arraybeing interspersed between the patterns imprinted by the first array.

According to a second aspect of the present invention, there is providedan imprint lithography apparatus comprising a first array of templateholders, a second array of template holders, and a substrate tablearranged to support a substrate to be imprinted, wherein the first arrayof template holders is arranged to hold an array of imprint templatesthat can be used to imprint a first array of patterns onto thesubstrate, and the second array of template holders is arranged hold anarray of imprint templates that can be used to imprint a second array ofpatterns onto the substrate, the patterns imprinted by the second arraybeing arranged in stripes which alternate between stripes formed bypatterns imprinted by the first array.

The first and second aspects of the invention may be arranged such thatthe entire useable surface of a substrate, or at least the majority ofthe usable surface, are imprinted by the imprint of the first and secondarrays of imprint templates. Alternatively, third and possibly fourthsuitably arranged imprint templates may in addition be used.

According to a third aspect of the present invention, there is providedan imprint lithography apparatus comprising an array of templateholders, wherein a given template holder, arranged to imprint a givenarea, falls within a footprint which does not extend into each adjacentimprint area, but instead extends into only a subset of adjacent imprintareas.

According to a fourth aspect of the present invention, there is providedan imprint lithography apparatus comprising an array of templateholders, wherein a given template holder, arranged to imprint a givenarea, falls within a footprint which does not extend beyond a midwaypoint of adjacent imprint areas.

According to a fifth aspect of the present invention, there is provideda method of imprint lithography comprising imprinting a first array ofpatterns onto a substrate, then imprinting a second array of patternsonto the substrate, the patterns of the second array being interspersedbetween the patterns of the first array.

According to a sixth aspect of the present invention, there is providedan imprint template to imprint a pattern onto a substrate, the imprinttemplate comprising a lens arranged to direct radiation through theimprint template such that the radiation reaches substantially allregions of a substrate which is to be exposed to the radiation.

According to a seventh aspect of the present invention, there isprovided a support to hold an imprint template, the support comprising alens arranged to direct radiation towards the imprint template with adesired intensity distribution.

The lens referred to in the sixth and seventh aspects of the inventionmay be plano-convex or plano-concave. The lens may be provided in anuppermost surface of the imprint template. The support may be arrangedto hold a template holder which in turn is arranged to hold the imprinttemplate.

According to an eighth aspect of the present invention, there isprovided an imprint lithography apparatus comprising an imprint templateand a substrate table arranged to support a substrate to be imprinted,wherein the imprint template is provided with at least part of analignment system.

According to a ninth aspect of the present invention, there is providedan imprint lithography apparatus comprising a template holder and asubstrate table arranged to support a substrate to be imprinted, whereinthe template holder is provided with at least part of an alignmentsystem.

The alignment system referred to in the eighth and ninth aspects of theinvention may comprise an image sensor.

One or more embodiments of the present invention are applicable to anyimprint lithography process in which a patterned template is imprintedinto an imprintable medium in a flowable state, and for instance can beapplied to hot and UV imprint lithography as described herein. For thepurpose of understanding one or more embodiments of the presentinvention, it is not necessary to describe the imprint process in anymore detail than has already been given and is known in the art.

4. BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying schematic drawings in whichcorresponding reference symbols indicate corresponding parts, and inwhich:

FIG. 1 a-1 c illustrate examples of conventional soft, hot and UVlithography processes respectively;

FIG. 2 illustrates a two step etching process employed when hot and UVimprint lithography is used to pattern a resist layer;

FIG. 3 schematically illustrates a template and a typical imprintableresist layer deposited on a substrate;

FIG. 4 schematically illustrates a substrate which has been imprinted byimprint templates according to an embodiment of the invention;

FIG. 5 schematically illustrates a substrate imprinting method accordingto an embodiment of the invention;

FIGS. 6 to 8 schematically illustrate imprint templates according to anembodiment of the invention; and

FIG. 9 schematically illustrates substrates which have been imprinted byarrays of imprint templates according to an embodiment of the invention.

5. DETAILED DESCRIPTION

There are two principal approaches to imprint lithography which will betermed generally as hot imprint lithography and UV imprint lithography.There is also a third type of “printing” lithography known as softlithography. Examples of these are illustrated in FIGS. 1 a to 1 c.

FIG. 1 a schematically depicts the soft lithography process whichinvolves transferring a layer of molecules 11 (typically an ink such asa thiol) from a flexible template 10 (typically fabricated frompolydimethylsiloxane (PDMS)) onto a resist layer 13 which is supportedupon a substrate 12 and planarization and transfer layer 12′. Thetemplate 10 has a pattern of features on its surface, the molecularlayer being disposed upon the features. When the template is pressedagainst the resist layer, the layer of molecules 11 stick to the resist.Upon removal of the template from the resist, the layer of molecules 11stick to the resist, the residual layer of resist is etched such thatthe areas of the resist not covered by the transferred molecular layerare etched down to the substrate.

The template used in soft lithography may be easily deformed and maytherefore not be suited to high resolution applications, e.g. on ananometer scale, since the deformation of the template may adverselyaffect the imprinted pattern. Furthermore, when fabricating multiplelayer structures, in which the same region will be overlaid multipletimes, soft imprint lithography may not provide overlay accuracy on ananometer scale.

Hot imprint lithography (or hot embossing) is also known as nanoimprintlithography (NIL) when used on a nanometer scale. The process uses aharder template made from, for example, silicon or nickel, which aremore resistant to wear and deformation. This is described for instancein U.S. Pat. No. 6,482,742 and illustrated in FIG. 1 b. In a typical hotimprint process, a solid template 14 is imprinted into a thermosettingor a thermoplastic polymer resin 15, which has been cast on the surfaceof a substrate 12. The resin may, for instance, be spin coated and bakedonto the substrate surface or more typically (as in the exampleillustrated) onto a planarization and transfer layer 12′. It should beunderstood that the term “hard” when describing an imprint templateincludes materials which may generally be considered between “hard” and“soft” materials, such as for example “hard” rubber. The suitability ofa particular material for use as an imprint template is determined byits application requirements.

When a thermosetting polymer resin is used, the resin is heated to atemperature such that, upon contact with the template, the resin issufficiently flowable to flow into the pattern features defined on thetemplate. The temperature of the resin is then increased to thermallycure (e.g. crosslink) the resin so that it solidifies and irreversiblyadopts the desired pattern. The template may then be removed and thepatterned resin cooled.

Examples of thermoplastic polymer resins used in hot imprint lithographyprocesses are poly (methyl methacrylate), polystyrene, poly (benzylmethacrylate) or poly (cyclohexyl methacrylate). The thermoplastic resinis heated so that it is in a freely flowable state immediately prior toimprinting with the template. It is typically necessary to heatthermoplastic resin to a temperature considerably above the glasstransition temperature of the resin. The template is pressed into theflowable resin and sufficient pressure is applied to ensure the resinflows into all the pattern features defined on the template. The resinis then cooled to below its glass transition temperature with thetemplate in place whereupon the resin irreversibly adopts the desiredpattern. The pattern will consist of the features in relief from aresidual layer of the resin which may then be removed by an appropriateetch process to leave only the pattern features.

Upon removal of the template from the solidified resin, a two-stepetching process is typically performed as illustrated in FIGS. 2 a to 2c. The substrate 20 has a planarization and transfer layer 21immediately upon it, as shown in FIG. 2 a. The purpose of theplanarization and transfer layer is twofold. It acts to provide asurface substantially parallel to that of the template, which helpsensure that the contact between the template and the resin is parallel,and also to improve the aspect ratio of the printed features, asdescribed herein.

After the template has been removed, a residual layer 22 of thesolidified resin is left on the planarization and transfer layer 21,shaped in the desired pattern. The first etch is isotropic and removesparts of the residual layer 22, resulting in a poor aspect ratio offeatures where L1 is the height of the features 23, as shown in FIG. 2b. The second etch is anisotropic (or selective) and improves the aspectratio. The anisotropic etch removes those parts of the planarization andtransfer layer 21 which are not covered by the solidified resin,increasing the aspect ratio of the features 23 to (L2/D), as shown inFIG. 2 c. The resulting polymer thickness contrast left on the substrateafter etching can be used as for instance a mask for dry etching if theimprinted polymer is sufficiently resistant, for instance as a step in alift-off process.

Hot imprint lithography suffers from a disadvantage in that not only isthe pattern transfer performed at a higher temperature, but alsorelatively large temperature differences might be required in order toensure the resin is adequately solidified before the template isremoved. Temperature differences between 35 and 100° C. may be needed.Differential thermal expansion between, for instance, the substrate andtemplate may then lead to distortion in the transferred pattern. Thismay be exacerbated by the relatively high pressure needed for theimprinting step, due the viscous nature of the imprintable material,which can induce mechanical deformation in the substrate, againdistorting the pattern.

UV imprint lithography, on the other hand, does not involve such hightemperatures and temperature changes nor does it require such viscousimprintable materials. Rather, UV imprint lithography involves the useof a partially or wholly transparent template and a UV-curable liquid,typically a monomer such as an acrylate or methacrylate. for example. UVimprint lithography is discussed, for example, in J. Haisma“Mold-assisted nanolithography: A process for reliable patternreplication”, J. Vac. Sci. Technol. B 14(6), November/December 1996. Ingeneral, any photopolymerizable material could be used, such as amixture of monomers and an initiator. The curable liquid may also, forinstance, include a dimethyl siloxane derivative. Such materials areless viscous than the thermosetting and thermoplastic resins used in hotimprint lithography and consequently move much faster to fill templatepattern features. Low temperature and low pressure operation also favorshigher throughput capabilities. Although the name ‘UV imprintlithography’ implies that UV radiation is always used, those skilled inthe art will be aware that any suitable actinic radiation may be used(for example, visible light may be used). Hence, any reference herein toUV imprint lithography, UV radiation, UV curable materials, etc. shouldbe interpreted as including any suitable actinic radiation, and shouldnot be interpreted as being limited to UV radiation only.

An example of a UV imprint process is illustrated in FIG. 1 c. A quartztemplate 16 is applied to a UV curable resin 17 in a similar manner tothe process of FIG. 1 b. Instead of raising the temperature as in hotembossing employing thermosetting resins, or temperature cycling whenusing thermoplastic resins, UV radiation is applied to the resin throughthe quartz template in order to polymerize and thus cure it. Uponremoval of the template, the remaining steps of etching the residuallayer of resist are the same or similar as for the hot embossing processdescribed herein. The UV curable resins typically used have a much lowerviscosity than typical thermoplastic resins so that lower imprintpressures can be used. Reduced physical deformation due to the lowerpressures, together with reduced deformation due to high temperaturesand temperature changes, makes UV imprint lithography suited toapplications requiring high overlay accuracy. In addition, thetransparent nature of UV imprint templates can accommodate opticalalignment techniques simultaneously to the imprinting.

Although this type of imprint lithography mainly uses UV curablematerials, and is thus generically referred to as UV imprintlithography, other wavelengths of radiation may be used to cureappropriately selected materials (e.g., activate a polymerization orcross linking reaction). In general, any radiation capable of initiatingsuch a chemical reaction may be used if an appropriate imprintablematerial is available. Alternative “activating radiation” may, forinstance, include visible light, infrared radiation, x-ray radiation andelectron beam radiation. In the general description herein, referencesto UV imprint lithography and use of UV radiation are not intended toexclude these and other activating radiation possibilities.

As an alternative to imprint systems using a planar template which ismaintained substantially parallel to the substrate surface, rollerimprint systems have been developed. Both hot and UV roller imprintsystems have been proposed in which the template is formed on a rollerbut otherwise the imprint process is very similar to imprinting using aplanar template. Unless the context requires otherwise, references to animprint template include references to a roller template.

There is a particular development of UV imprint technology known as stepand flash imprint lithography (SFIL) which may be used to pattern asubstrate in small steps in a similar manner to optical steppersconventionally used, for example, in IC manufacture. This involvesprinting small areas of the substrate at a time by imprinting a templateinto a UV curable resin, ‘flashing’ UV radiation through the template tocure the resin beneath the template, removing the template, stepping toan adjacent region of the substrate and repeating the operation. Thesmall field size of such step and repeat processes may help reducepattern distortions and CD variations so that SFIL may be particularlysuited to manufacture of IC and other devices requiring high overlayaccuracy. United States patent application publication US 2004-0124566describes in detail an example of a step and flash imprint lithographyapparatus.

Although in principle the UV curable resin can be applied to the entiresubstrate surface, for instance by spin coating, this may be problematicdue to the volatile nature of UV curable resins.

One approach to addressing this problem is the so-called ‘drop ondemand’ ink jet type printing process in which the resin is dispensedonto a target portion of the substrate in droplets immediately prior toimprinting with the template. The liquid dispensing is controlled sothat a certain volume of liquid is deposited on a particular targetportion of the substrate. The liquid may be dispensed in a variety ofpatterns and the combination of carefully controlling liquid volume andplacement of the pattern can be employed to confine patterning to thetarget area.

Dispensing the resin on demand as mentioned is not a trivial matter. Thesize and spacing of the droplets are carefully controlled to ensurethere is sufficient resin to fill template features while at the sametime minimizing excess resin which can be rolled to an undesirably thickor uneven residual layer since as soon as neighboring drops touch fluid,the resin will have nowhere to flow.

Although reference is made herein to depositing UV curable liquids ontoa substrate, the liquids could also be deposited on the template and ingeneral the same techniques and considerations will apply.

FIG. 3 illustrates the relative dimensions of the template, imprintablematerial (curable monomer, thermosetting resin, thermoplastic, etc) andsubstrate. The ratio of the width of the substrate, D, to the thicknessof the curable resin layer, t, is of the order of 10⁶. It will beappreciated that, in order to avoid the features projecting from thetemplate damaging the substrate, the dimension t should be greater thanthe depth of the projecting features on the template.

The residual layer left after stamping is useful in protecting theunderlying substrate, but as mentioned herein it may also be the sourceof a problem, particularly when high resolution and/or minimum CD(critical dimension) variation is desired. The first ‘breakthrough’ etchis isotropic (non-selective) and will thus to some extent erode thefeatures imprinted as well as the residual layer. This may beexacerbated if the residual layer is overly thick and/or uneven. Thisproblem may, for instance, lead to variation in the thickness of linesultimately formed in the underlying substrate (i.e. variation in thecritical dimension). The uniformity of the thickness of a line that isetched in the transfer layer in the second anisotropic etch is dependantupon the aspect ratio and integrity of the shape of the feature left inthe resin. If the residual resin layer is uneven, then the non-selectivefirst etch can leave some of these features with “rounded” tops so thatthey are not sufficiently well defined to ensure good uniformity of linethickness in the second and any subsequent etch process. In principle,the above problem may be reduced by ensuring the residual layer is asthin as possible but this can require application of undesirably largepressures (possibly increasing substrate deformation) and relativelylong imprinting times (possibly reducing throughput).

The template is a significant component of the imprint lithographysystem. As noted herein, the resolution of the features on the templatesurface is a limiting factor on the attainable resolution of featuresprinted on the substrate. The templates used for hot and UV lithographyare generally formed in a two-stage process. Initially, the desiredpattern is written using, for example, electron beam writing (e.g., withan electron beam pattern generator), to give a high resolution patternin resist. The resist pattern is then transferred into a thin layer ofchrome which forms the mask for the final, anisotropic etch step totransfer the pattern into the base material of the template. Othertechniques such as for example ion-beam lithography, X-ray lithography,extreme UV lithography, epitaxial growth, thin film deposition, chemicaletching, plasma etching, ion etching or ion milling could be used.Generally, a technique capable of very high resolution will be used asthe template is effectively a 1× mask with the resolution of thetransferred pattern being limited by the resolution of the pattern onthe template.

The release characteristics of the template may also be a consideration.The template may, for instance, be treated with a surface treatmentmaterial to form a thin release layer on the template having a lowsurface energy (a thin release layer may also be deposited on thesubstrate).

Another consideration in the development of imprint lithography is themechanical durability of the template. The template may be subjected tolarge forces during stamping of the resist, and in the case of hotlithography, may also be subjected to extremes of pressure andtemperature. This may cause wearing of the template, and may adverselyaffect the shape of the pattern imprinted upon the substrate.

In hot imprint lithography, there is a potential advantage in using atemplate of the same or similar material to the substrate to bepatterned in order to reduce differential thermal expansion between thetwo. In UV imprint lithography, the template is at least partiallytransparent to the activation radiation and accordingly quartz templatesare used.

Although specific reference may be made in this text to the use ofimprint lithography in the manufacture of ICs, it should be understoodthat imprint apparatus and methods described may have otherapplications, such as the manufacture of integrated optical systems,guidance and detection patterns for magnetic domain memories, hard discmagnetic media, flat panel displays, thin-film magnetic heads, etc.

While in the description herein, particular reference has been made tothe use of imprint lithography to transfer a template pattern to asubstrate via an imprintable resin effectively acting as a resist, insome circumstances the imprintable material may itself be a functionalmaterial, for instance having a functionally such as electrical orthermal conductivity, optical linear or non-linear response, amongothers. For example, the functional material may form a conductivelayer, a semi-conductive layer, a dielectric layer or a layer havinganother desirable mechanical, electrical or optical property. Someorganic substances may also be appropriate functional materials. Suchapplications may be within the scope an embodiment of the presentinvention.

FIG. 4 shows schematically an arrangement whereby imprinting of apattern onto a substrate may be performed quickly by imprinting largeareas of the substrate at a time. The substrate 100 is imprinted withimprint areas 102. Each imprint area 102 may include a plurality ofdies, with each die for example being separated from adjacent dies byscribe lanes. Individual dies are not illustrated in FIG. 4. The streets110 between the imprint areas 102 may be used for process controlpurposes, and may also be used as scribe lanes. Referring to FIG. 5, aprocess whereby the imprint areas 102 may be imprinted onto thesubstrate 100 will now be described. A substrate 100 is provided, whichsubstrate is typically either sufficiently flat to receive an imprinttemplate or provided with a polished planarization layer. The substrate100 is placed on a substrate table, which is movable in the x and ydirections using electrical motors (the substrate table and motors arenot illustrated for ease of understanding). In some instances theflatness of the substrate 100 may be measured by a sensor, and thesubstrate table may be adjusted to eliminate or reduce measuredunflatness.

UV curable imprintable medium is inkjet printed onto some imprint areas102 a on the substrate 100 (delineated schematically by dotted lines).Other imprint areas 102 b are not provided with imprintable medium, forreasons that will be explained below. The imprintable medium may beprovided as discrete droplets 112 as shown schematically in FIG. 5 a.

The provision of the imprintable medium 112 may conveniently be achievedby moving the substrate 100 to a different location using the motorswhich control the position of the substrate table. The imprintablemedium may be provided by, for example, a stationary mounted single ormulti-nozzle print head, or an ensemble of single or multi-nozzle printheads.

Once the imprintable medium 112 has been applied, the substrate may bemoved to a different location in order to receive one or more imprinttemplates. It will be appreciated that in an alternative arrangement thesubstrate is not moved, and that the one or more imprint templates aremoved to the location of the substrate. In a further alternativearrangement neither the substrate nor the imprint templates are moved todifferent locations.

Referring to FIG. 5 b, imprint templates 114 held by template holders115 are pressed against the substrate 100. It can be seen from FIG. 5 bthat the template holders occupy a significant amount of space, suchthat there is not sufficient space to provide an imprint template toimprint every imprint area 102 a, 102 b at the same time.

The imprint templates 114 are provided with sharp edges 113 which act toinhibit the imprintable medium 112 from flowing out from underneath theimprint templates. This is due to surface tension which pins theimprintable medium 112 at the sharp edges 113. Once the imprintablemedium 112 has completely filled gaps between the imprint templates 114and the substrate 100, the imprint template is prevented from movingfurther towards the substrate. This is because the surface tensioninhibits the imprintable medium 112 from flowing out from underneath theimprint templates 114.

Referring to FIG. 5 c, ultraviolet radiation 120 is directed to theimprintable medium 112 between the imprint templates 114 and thesubstrate 100. The imprint templates 114 are substantially transparentto ultraviolet radiation, and therefore transmit the ultravioletradiation to the imprintable medium 112. The imprintable medium 112 ispolymerized and solidified by the ultraviolet radiation 120. In onearrangement, the ultraviolet radiation may be provided at a dedicatedlocation within the lithographic apparatus, the substrate 100 andtemplates 114 being moved to that location to allow it to be illuminatedby the ultraviolet radiation, and then subsequently moved to a differentlocation. In an alternative arrangement, the ultraviolet radiation maybe administered to the imprintable medium 112 on the substrate 100without moving the substrate to a different location.

Referring to FIG. 5 d, the imprint templates 114 are removed from thesubstrate 100, leaving behind a patterned layer of polymerizedimprintable medium 112. The imprint process is then repeated, to allowpatterns to be imprinted onto the remaining imprint areas (e.g. 102 b).

In some instances it may be desired to provide imprint templates veryclose to one another, i.e. with a street size which is very narrow (forexample as little as 100 microns). A suitable imprint template forachieving this is shown schematically in FIG. 6. Referring to FIG. 6, animprint template 114 may be provided with gripping handles 130 at aperimeter of the imprint template. The gripping handles 130 allow atemplate holder (not illustrated) to securely engage with the imprinttemplate 114.

To ensure that ultraviolet radiation 120 passes to imprintable mediumlocated beneath all parts of the imprint template 114, an uppermostsurface of the imprint template is provided with a plano-convex lens132. As shown schematically in FIG. 6, the plano-convex lens 132 directsthe ultraviolet radiation 120 to all parts of a lowermost surface of theimprint template 114.

The method described above is particularly suited for imprinting a firstpatterned layer onto a substrate. Where this is done, there is norequirement to align the pattern to a pattern previously provided on thesubstrate. Some low accuracy knowledge of the position of the substrate100 is useful in order to ensure that the areas of imprintable medium112 and the streets of anti-wetting coating 110 are correctly located,and for example do not overlap with one another.

FIG. 7 shows schematically an imprint template 214 which may be used toimprint a pattern which is aligned with a pattern previously provided ona substrate. FIG. 7 a is a cross-section of the imprint template 214,and FIG. 7 b is the imprint template 214 from below. In order tofacilitate understanding of the embodiment of the invention, the crosssection shown in FIG. 7 a is not strict, rather includes elements thatwould not be visible in a strict cross section.

The imprint template 214 is attached to a template holder 240, and has alowermost surface which is provided with a pattern 242. The imprinttemplate 214 and template holder 240 are attached via four actuators 244(of which one is shown in FIG. 7 a and all four shown in FIG. 7 b) to asupport 246. The actuators 244 are, for example, piezoelectricactuators, and are capable of movement in the z-direction. The actuators244 will hereafter be referred to as imprint actuators 244. The imprinttemplate 214 is constructed from quartz, fused silica or optical gradepolyolefin. The template holder is made from stress free stainless steelor a high quality grade aluminum. The imprint template 214 is supportedby comb hinges 261 and a comb-like structure 263, and is connected viapiezoelectric actuators 262, which are capable of movement in the x andy directions, to the template holder 240. The form of the imprinttemplate 214 can be adapted to elastically by the piezoelectricactuators 262. The piezoelectric actuators 262 will hereafter bereferred to as alignment actuators 262.

A central region of the imprint template 214 is provided with aplano-concave lens 232. A correspondingly dimensioned central portion ofthe template holder 240 is cut away to provide an opening 248. A centralportion of the support 246 is provided with an opening 250, within whichis a plano-concave lens 252. The opening 250 in the support 246 issubstantially co-axial with the opening 248 in the template holder 240.

Four cylindrical bores 254 are provided in the template holder 240 andthe support structure 246. An optics holding container of an alignmentsystem 255 is provided in each cylindrical bore 254 (plus associatedtransversely oriented recesses). The alignment system 255 comprises aradiation source 258 and a semi-transparent mirror 260 arranged todirect radiation through alignment optics (not shown) in the opticsholding container(s). The radiation source 258 may, for example,comprise a light emitting diode, or may alternatively be a white lightsource. A CCD camera 264 is located above the semi-transparent mirror260 above the alignment optics. The CCD camera receives radiation whichhas passed through the alignment optics onto a substrate 200, and hasbeen reflected back through the alignment optics and through thesemi-transparent mirror 260. It will be appreciated that the CCD camerais an example of an image sensor, and other suitable image sensors maybe used. Alignment and magnification correction are guided by alignmentmarks 272 on the substrate 100 and corresponding alignment marks 271 onthe imprint template 214.

The alignment system 255 allows for high precision alignment of theimprint template pattern 242 with a pattern previously provided on thesubstrate 200, using the alignment actuators 262.

Operation of the imprint template 214 shown in FIG. 7 will now bedescribed. It should be borne in mind that several imprint templates maybe provided on the support 246. Indeed, a sufficient number of imprinttemplates may be provided to allow an entire substrate to be imprintedat one time.

Imprintable medium 270 is applied to the substrate 200, for exampleusing ink jet printing to provide the imprintable medium in a certainpattern. This may be done by using a substrate table 274 to move thesubstrate 200 to another location, for example an imprintable mediumapplication location. Further different locations may be used to measurethe flatness of the substrate 200, and to imprint a pattern onto thesubstrate.

The substrate 200 is then located beneath the imprint template 214. Theimprint template 214 is moved downwards and/or the substrate 200 ismoved upwards until the imprint template is located around 10 micronsabove the substrate 200. The imprint actuators 244 push the imprinttemplate 214 onto the substrate 200 with a controlled force. At themoment the imprint layer is completely formed the force needed to pushthe template further down increases considerably. This is because sharpedges 230 of the imprint template 214 inhibit imprintable medium fromflowing beyond the imprint template. This change in force is used in aclosed loop control set-up for leveling the imprint template 214 withrespect to the substrate 200.

When the gap between the imprint template 214 and the substrate 200 issufficiently small, alignment marks 272 provided on the substrate 200and the corresponding alignment marks 271 on the imprint template 214are both in focus and recorded by the alignment optics 255 and the CCDcamera 264. Alignment of the imprint template 214 to the substratealignment marks 272 is then performed. This is done by comparing thelocation of substrate alignment marks 272 with fiducial alignment marks271 using the CCD camera 264, and actuating the alignment actuators 262in the x and y directions appropriately. Some movement of the imprintactuators 244 may also be used during alignment. Some elasticdeformation of the imprint template 214 and the template holder 240 willtake place. The elastic deformation is such that the flatness of thelowermost surface of the imprint template 214 is not significantlychanged.

Where three or more alignment marks located at different positions onthe substrate 200 are used, adjustment by the alignment actuators 262may include magnification correction (i.e. making the imprint template214 larger or smaller).

Once alignment of the imprint template 214 to the substrate 200 has beencompleted, ultraviolet radiation 266 is directed through the imprinttemplate onto the imprintable medium 270, such that the imprintablemedium polymerizes and solidifies. The ultraviolet radiation 266 passesthrough the opening 250, through the plano-concave lens 252 and theplano-concave lens 232. The ultraviolet radiation then passes via theimprint template 214 onto the imprintable medium 270 provided on thesubstrate 200. The ultraviolet radiation has an intensity distributionwhich is arranged such that the intensity of ultraviolet radiationincident upon the imprintable medium 270 is substantially uniform. Theintensity of the UV beam on passing into the support 246 is lower at acentral portion of the radiation and has a higher intensity at itsedges, such that when the ultraviolet radiation is directed outwards bythe lenses 252, 232 the intensity of the ultraviolet radiation becomessubstantially uniform.

Once the imprintable medium 270 has polymerized and solidified, theimprint template is removed from the substrate 200 by using the imprintactuators 244 to draw the imprint template 214 upwards. The solidifiedimprintable medium 270 retains a pattern imprinted by the imprinttemplate 214.

Although only one imprint template 214 is visible in FIG. 7, it will beunderstood that a plurality of imprint templates may be providedtogether. For example, sufficient imprint templates may be provided toallow an entire substrate to be imprinted with a pattern at one time.

Although FIG. 7 shows parts of the alignment system 255 as being locatedin the template holder 240, it will be appreciated that the alignmentsystem may provided in different locations. For example, the alignmentsystem may be provided in the template holder only, the template holderbeing arranged such that it extends along sides of the imprint template214. In a further example, the alignment system may be provided in thetemplate holder and the support 246.

FIG. 8 shows an alternative template holder 280. The template holder 280is fabricated from Zerodur ceramic (made by Schott A.G.), but may befabricated from any other suitable material. The template holder 280 isprovided with a channel 281 through which a low pressure is appliedwhich is used to hold an imprint template 282. Piezo actuators 283 areprovided in recesses 284 located on either side of the imprint template282. The piezo actuators 283 are connected between different parts ofthe template holder, and may be used to stretch or compress the templateholder 280 in the x and y directions. This in turn stretches orcompresses the imprint template 282. This may be done in order to matchthe imprint template 282 to a pattern already present on a substrate tobe imprinted. A plurality of piezo actuators may be provided to eachside of the imprint template 282. This will assist in adjusting theimprint template to match, for example, distortion present in thepattern on the substrate. The template holder 280 may be provided withone or more of the features described above in relation to FIG. 7.

The separation between adjacent areas to be imprinted may be small, forexample around 100 microns or less, and this may render it difficult toindividually attach all imprint templates to, for example, a support(there may not be sufficient space for suitable attachment means to beprovided). A further or alternative problem which may arise is that theforces required in order to remove all of the imprint templates from thesubstrate following polymerization of the imprintable medium may be solarge that they cause the substrate to become damaged.

A template holder may extend laterally into adjacent regions which areto be imprinted. Referring to FIG. 9 a, a template holder 301 may bearranged such that it only extends into four adjacent regions, and doesnot extend beyond the center of those regions, i.e., occupy as muchspace so as to extend almost halfway into the neighboring imprintfields. This allows an array of template holders (and associated imprinttemplates) to be used at the same time to imprint into an array ofregions. Dark gray/black shading is used in FIG. 9 a to indicate theregions that may be imprinted simultaneously.

Four imprints are required in order to substantially fully cover thesurface of a substrate 300, and these are illustrated schematically inFIGS. 9 a to 9 d. Following the first imprint, regions which arediagonally adjacent the imprinted regions are imprinted using a secondarray of imprint templates, as shown in FIG. 9 b. To aid understanding,the regions that are currently being imprinted are represented in darkgray/black, the regions that have already been imprinted are representedin intermediate gray, and the regions not yet imprinted are representedby light gray.

A third imprint, by a third array of imprint templates, is representedin FIG. 9 c, dark gray/black again being used to represent those regionsthat are currently being imprinted, intermediate gray again being usedto represent regions that have already been imprinted, and light grayagain being used to represent regions not yet imprinted. A fourthimprint by a fourth array of imprint templates is represented in FIG. 9d, dark gray/black again being used to represent those regions that arecurrently being imprinted and intermediate gray again being used torepresent regions that have already been imprinted.

Each of the imprints shown in FIGS. 9 a to 9 d may be performed bymoving each array of imprint templates in turn to be over the substrate300 and then imprinting the substrate. Alternatively, the arrays ofimprint templates may remain in specific locations, with the substratebeing moved between the arrays of imprint templates. Where this is done,imprinting may be performed in parallel, for example with a firstsubstrate being imprinted by the first array of imprint templates, andthe second substrate being imprinted by the second array of imprinttemplates, etc. A combination of moving the arrays of imprint templatesand moving the substrates may also be used (for example, allowing twosubstrates to be imprinted in parallel rather than four).

It is not essential that the template holder exactly occupies the spaceillustrated in FIG. 9. Rather, it is preferred that the template holderfalls within a footprint defined by the shape shown in FIG. 9 (thetemplate holders may, for example, be smaller than the shape).

It will be understood by those skilled in the art that the templateholders may be designed such that they occupy spaces which differ fromthose illustrated in FIG. 9. For example, the template holder shown inFIG. 9 a may be rotated through 45 degrees, such that it does notoverlap with diagonally adjacent regions. Alternatively, the templateholder may be provided on only two sides of the imprint template, forexample such that it extends into only two adjacent regions. Otheralternative sizes and shapes of the spaces occupied by the templateholder will be apparent to those skilled in the art. In some instances adifferent number of imprints being required.

The imprint templates referred to above may, for example, be constructedfrom optical grade polyolefin or, if only very small elastic deformationof the imprint template is desired, from quartz glass. The patternprovided in an imprint template may be written by an electron beampattern generator in resist, followed by an etch step. An alternativemethod of making an imprint template comprises using an electron beampattern generator to provide a pattern on a nickel stamp, then usingprecision injection molding to form the imprint templates. This issimilar to the manufacturing process used to make compact discs. Theplano-concave lens 132 and gripping handles 130 shown in FIG. 6, may beincluded when injection molding the imprint template.

Although the above description refers to ultraviolet radiation it willbe appreciated that, as explained further above, any suitable actinicradiation may be used.

While specific examples of the invention have been described above, itwill be appreciated that the present invention may be practicedotherwise than as described. The description is not intended to limitthe invention.

1. An imprint lithography apparatus comprising a first array of templateholders, a second array of template holders, and a substrate tablearranged to support a substrate to be imprinted, wherein the first arrayof template holders is arranged to hold an array of imprint templatesthat can be used to imprint a first array of patterns onto thesubstrate, and the second array of template holders is arranged to holdan array of imprint templates that can be used to imprint a second arrayof patterns onto the substrate, the patterns imprinted by the secondarray being interspersed between the patterns imprinted by the firstarray.
 2. The apparatus of claim 1, wherein the apparatus furthercomprises a third array of template holders arranged to hold an array ofimprint templates that can be used to imprint a third array of patternsonto the substrate, the patterns imprinted by the third array beinginterspersed between the patterns imprinted by the first and secondarrays.
 3. The apparatus of claim 2, wherein the apparatus furthercomprises a fourth array of template holders arranged to hold an arrayof imprint templates that can be used to imprint a fourth array ofpatterns onto the substrate, the patterns imprinted by the fourth arraybeing interspersed between the patterns imprinted by the first, secondand third arrays.
 4. The apparatus of claim 1, wherein the first andsecond arrays of template holders are in fixed locations, and thesubstrate is moveable between the first and second arrays.
 5. Theapparatus of claim 2, wherein the first, second and third arrays oftemplate holders are in fixed locations, and the substrate is moveablebetween the first, second and third arrays.
 6. The apparatus of claim 1,further comprising imprint templates held by the arrays of templateholders, at least some of the imprint templates each comprising a lensarranged to direct radiation through the imprint template such that theradiation reaches substantially all regions of a substrate which is tobe exposed to the radiation.
 7. The apparatus of claim 6, wherein thelens is a plano-concave lens.
 8. The apparatus of claim 6, wherein thelens is provided in an uppermost surface of the imprint template.
 9. Theapparatus of claim 1, further comprising a support configured to holdthe template holders, the support comprising a plurality of lensesarranged to direct radiation towards the imprint template with a desiredintensity distribution.
 10. The apparatus of claim 9, wherein the lensesare plano-concave lenses.
 11. The apparatus of claim 1, furthercomprising imprint templates held by the arrays of template holders, atleast some of the imprint templates each comprising at least part of analignment system.
 12. The apparatus of claim 11, wherein the alignmentsystem comprises an image sensor.
 13. The apparatus of claim 1, whereinat least some of the template holders comprise at least part of analignment system.
 14. The apparatus of claim 13, wherein the alignmentsystem comprises an image sensor.
 15. An imprint lithography apparatuscomprising an array of template holders, wherein a given templateholder, arranged to imprint a given area, falls within a footprint whichdoes not extend into each adjacent imprint area, but instead extendsinto only a subset of adjacent imprint areas.
 16. The apparatus of claim15, wherein the footprint of the given template holder does not extendbeyond a midway point of each adjacent imprint area.
 17. The apparatusof claim 15, further comprising imprint templates held by the array oftemplate holders, at least some of the imprint templates each comprisinga lens arranged to direct radiation through the imprint template suchthat the radiation reaches substantially all regions of a substratewhich is to be exposed to the radiation.
 18. The apparatus of claim 15,wherein at least some of the template holders comprise at least part ofan alignment system.
 19. An imprint lithography apparatus comprising anarray of template holders, wherein a given template holder, arranged toimprint a given area, falls within a footprint which does not extendbeyond a midway point of adjacent imprint areas.
 20. The apparatus ofclaim 19, further comprising imprint templates held by the array oftemplate holders, at least some of the imprint templates each comprisinga lens arranged to direct radiation through the imprint template suchthat the radiation reaches substantially all regions of a substratewhich is to be exposed to the radiation.
 21. The apparatus of claim 19,wherein at least some of the template holders comprise at least part ofan alignment system.